1. Field of the Invention
The present invention relates to an X-ray diagnostic apparatus for allowing stereoscopic visualization of X-ray images, e.g., angiograms of an object under examination.
2. Description of the Prior Art
In a conventional X-ray diagnostic apparatus set forth in the preamble, there are usually provided two X-ray tubes, or a single X-ray tube having two X-ray radiation sources. An object under examination, e.g., a patient is radiated by the X-rays by alternately energizing those two X-ray tubes or two radiation sources. Those X-rays penetrate through the object and are incident upon a visual image converter such as an X-ray image intensifier. The image converter converts the X-ray transmission images into visual X-ray images. Those visual X-ray images are received by an image senser, e.g., a television camera to be converted into X-ray image signals. The X-ray image signals are electrically processed in a digital subtraction circuit so as to obtain angiographic images of the object.
To realize better stereoscopic visualization of the angiographic images, the image senser for receiving the X-ray transmission images must prevent an influence of the after-image phenomenon from the successive image conversion. That is, for example when the single image senser receives the succeeding transmission X-ray image before the after-image phenomenon of the preceeding transmission X-ray image still remains in the image senser, those transmission X-ray images are mixed up therein, so that the stereoscopic visualization is extremely deteriorated.
When a vidicon is employed as the pick-up tube of the above image senser, it practically requires at least 50 millisecond-time interval to avoid the influence of the after-image thereof. Accordingly, if a single vidicon TV camera is used, the time interval between the successive X-ray projections from the right and left X-ray sources need more than 50 milliseconds in order to prevent deterioration of the stereoscopic visualization by the vidicon that is caused by unnecessarily mixing the incident X-ray image with the previously stored image.
If time intervals of the X-ray projection become more than 50 milliseconds, the visual images of the object which have taken at two different projection angles have different shapes, or contours from each other in case that the shape of the object changes at a rapid speed, e.g., coronary arteries. Accordingly, it may cause quality of the stereoscopic visualization to be deteriorated.
In principle, such stereoscopic visualization can be achieved by observing simultaneously an object at two different angles of observation, or with a given parallax. The time intervals of the X-ray projection must be therefore chosen short as permitted as possible, because it is impossible to simultaneously project X-rays toward the object from two X-ray sources in the normal stereoscopic X-ray diagnostic apparatus. It is necessary to shorter the X-ray projection interval in order to achieve the stereoscopic visualization for the smooth movement of the moving portion of the object at a high speed.
Furthermore, the right view and the left view for the object under examination are optically and also electrically separated from each other.
To realize such better stereoscopic visualization by an X-ray diagnostic apparatus, one proposal is disclosed, e.g., in the Japanese unexamined (Kokai) patent application No. 58-104593 (1983). This proposal is that the first and second X-ray sources and television cameras are arranged in relation to the object for the stereoscopic visualization, and when, for instance, the first X-ray source is energized, the first television camera can receive the image, but simultaneously the image incident upon the second television camera is interrupted. That is, the first and second X-ray sources and TV cameras are alternately operated to prevent the influences of the after-images by not mixing with each other the sequential images incident upon the same TV camera.
Other problems are revealed from the conventional X-ray diagnostic apparatus. Since two TV cameras are employed, two complex and expensive optical systems optically coupled between the X-ray sources and the two TV cameras are necessary which usually include the half mirrors, two TV lenses and the electronics shutters. However, as those optical elements cause a loss of light to a considerable degree, various measures must be taken, e.g., use of a lens having a small aperture value, or a small "F" value.
Moreover, the electrical characteristics of those TV cameras are inherently different from each other, so that an adjustment for the electrical characteristics of the resultant video signals takes a long time and makes difficult. Those electrical characteristics of the TV cameras are known as the gamma characteristics, the deflection size and distortion, and the input/output signal characteristics. As a result, those difficulties, on the other hand, cause an expensive X-ray diagnostic apparatus in cost and a bulky apparatus.
It is therefore an object of the present invention to avoid and overcome the above-described problems by employing a single television camera in an X-ray diagnostic apparatus having two X-ray radiation sources for the stereoscopic visualization.